Understanding Neural Network What is a neural network? Figure 1: What is a Neural Network? The neural network is a system that mimics a human brain structure. Figure 1 presents a multi-layer feedforward Neural Network structure, which contains an input layer (green), hidden layers (pink) and an output layer (orange). Each layer contains multiple nodes indicated by a small circle, for example, input nodes are in green, hidden nodes are in pink, and output nodes are in orange. Nodes in different layers can connect to each other, and the connection strength between two nodes is called a weight between these nodes. The connection flow is started from the input layer to hidden layers, and then to the output layer. Each node in a hidden layer can accept input connections from a previously hidden layer or input layer. These input connections will be summed and fed to a special function called activation function to form its node's output. As a result, only hidden la